1. Field of the Invention
The present invention relates generally to printing systems and more particularly to a system that uses a plurality of printing cartridges for high-speed printing.
2. Description of the Background of the Invention
Ink jet printing systems use ink jet cartridges that propel a drop of ink to a substrate, such as paper. Some ink jet printing system use a traversing print head, where a print head traverses the width of the paper dropping one or more lines of ink to form a swath of an image along the width of the paper. Upon completion of the swath, the paper is advanced in accordance with the width of the swath and the print head traverses the width of the paper to print a next swath. Traversing head printing systems are generally slower and are used in applications where print speed is not of great importance.
Other ink jet printing systems use a single fixed printing head. The paper advances under the printing head and the nozzles of the printing head eject drops of ink onto the paper in accordance with the position with paper to print an image. These types of ink jet printing systems are capable of higher print speeds than printing systems which use traversing heads; however, these systems generally use a relatively narrow printing head and, thus are used in applications where a relatively narrow, 1 to 2 inches (2.54-5.08 cm), image is required. Printing heads with larger widths are not commonly used because of the complexity of manufacture and because the entire printing head has to be replaced if any nozzles therein fail.
To overcome the speed short comings of the traversing head printing systems and the print width limitations of the fixed head printing systems, printing systems have been developed that stitch images printed by multiple, small, fixed printing heads. Typical printing heads comprise nozzles and require more area than necessary for the nozzles. The additional area is needed for mounting points, ink delivery tubing, drive electronics, etc. As such, two printing heads that are to print adjoining portions of an image cannot simply be mounted onto a frame or a carrier abutted against one another. Instead, printing heads are typically mounted onto a carrier in a two dimensional fashion. FIG. 1 shows a carrier 100 having printing cartridges 102 A-F mounted thereon. Each of the printing cartridges 102-A through 102-F comprise print heads 104-A through 104-F, respectively, wherein, each print head comprises a number of nozzles controllable to print a swath of an image. Each nozzle in the printing cartridge is controlled individually to eject a drop of ink onto a substrate 106. In operation, the substrate 106 is transported past the printing cartridges 102 in the direction indicated by the arrow A, while the nozzles that comprise each print head 104 are controlled to eject ink onto the substrate to print a swath in a direction parallel to the paper transport direction (arrow A). The swaths are printed abutting one another to print a stitched image of width W1 (and represented in FIG. 1 by a line of text 108. The carrier shown in FIG. 1 has a length of D that is at least sufficient to accommodate the number of printing cartridges required to print an image of width W1. Typical printing cartridges are able to print between 1 to 1.5 inch (2.54-3.81 cm) swaths. Using such printing cartridges in the configuration shown in FIG. 1 would enable printing of images that have a width W1 of 6 to 9 inches (15.24-22.86 cm).
FIG. 2 shows an arrangement of printing cartridges 202 A-F and 204 A-F on a carrier 200 that has a length D for printing an image that has a width W2, that is twice the width of the image printed by the arrangement of printing cartridges shown in FIG. 1. Specifically, a first group of six printing cartridges 202 A-F prints a first portion of the image having a width W1 and a second group of six printing cartridges 204 A-F prints a second portion of the image that also has width W1. The two groups printing in concert can produce a stitched image with a width W2. As described above in connection with FIG. 1, the substrate 206 is transported past the carrier 200 in the direction shown by arrow A such that the nozzles comprising the printing cartridges 202 A-F and 204 A-F eject ink thereon to print an image (illustrated as the line of characters 208). The configuration of FIG. 2 enables printing of images that have a width W2 of between 12 and 18 inches (30.48-40.72 cm), (if each printing cartridge prints a swatch of between 1 to 1.5 inches, i.e., 2.54-3.81 cm).
The printing cartridges 202 A-F are typically distributed on the carrier 200 in the dimension parallel to the direction A such that the distance between centers of each pair of printing cartridges that print adjacent swaths of the image (e.g., printing cartridges 202-A and 202-B) is equal to the inter-head distance d1, which is the distance between adjacent printing cartridges. As shown in FIG. 2, printing cartridges 202-F and 204-A print adjacent swaths of the image; however, the distance between these printing cartridges is five times the inter-head distance d1 and, therefore, there are four printing cartridges between cartridge 202-F and 204-A in the direction parallel to arrow A.
Alignment errors or errors in the transport of the substrate 206 may cause a misalignment (i.e., a stitching error) between two swaths of an image that are stitched. If such a misalignment is relatively small, there may not be any perceptible error in the image of the stitched swaths printed by two printing cartridges, especially if the distance between the two printing cartridges is relatively small. In particular, if the distance between the pair of printing cartridges that print abutting swaths of an image is equal to the inter-head distance d1 then a misalignment error between the cartridges may not result in a perceptible error in the stitching error. As shown in FIG. 2, when the two printing cartridges that print abutting swaths are members of the same group (either 202 A-F or 204 A-F) of printing cartridges, the distance therebetween is d1 (and there are no cartridges between them). The possibility of a perceptible stitching error is significantly greater if the misalignment occurs between two printing cartridges that print abutting swaths, where the two printing cartridges are members of different groups (i.e., between printing cartridges 202-F and 204-A). Decreasing the distance between pairs printing cartridges that print abutting swaths of the image reduces this possibility of perceptible stitching error.